Hello, I coudn't find a thread talking about this issue so I'll try to ask here.
My guildies and I want to set our kyestones as high as posible for the next week ( in order to try to make a +15 to loot on December 5th), I was so sure about how to do it cos I saw that pattern in my keys ( you get -1 form the key you own in yout bag, not the highest dungeon you do ?), but my guildies did thought otherwise.

So, how does mythic keystones upgrade/downgrade system work? I mean, what does determinate what lvl keystone are you expected to get in your weekly chest?

I remember doing a +15 in August, left for some months, came back on mid October, and got a +14 key from my chest (from the +15 I did back in August I guess), since that, I've been running 10-11 the lastest weeks (never my key), but the key I've got every week is always -1 from the prior keystone I had in my bag. So, it has been downgraded from 14 till 8 this week (as I said, i never used my keys), taking 1 level every week. As an example, last week I did 10-11 (as usually) and got a +9 key in my bag, and now it is a +8.

Any help? Thanks in advance